To Hum or not to Hum?

Mark Korda · « **on:** 25 Feb 2017, 05:54 pm »

Dear Frank, Wayner and Mary too,
I'm on the verge of buying your Humdinger but I would like to ask you a question. To narrow it down I'm going to give you as much history as I can;
I'm not bragging but I have 3 amps. I won't ever let them go unless I get to hear the Ultravalve someday. They are the
1. A Dyna-35 I completely rebuilt a few years back in which I made a few goofs.I sent it to you with my errors fixed and it's been my Flagship amp ever since. Sounds fantastic but.....
2. A Dyna-ST-70 Purist Audio amp wired by Purist's Audios founder's Air Force buddy I met as a penpal in Audiomart in the early 80's. It uses the 12AX7's and runs with a .75 volt bias. I have not burned out a tube yet. The wiring is meticulus and it sounds fantastic, but....
3. I got this amp on E-bay and it kicks ass. The AA-32 Heathkit integrated tube amp 1964. All I have done is clean the controls and there is nary a click or pop. This was the same style of amp my father had in the family room before he bought a Sears Silvertone solid state console? There are no buts here because...........
That 10 watt aside Heathkit is dead silent when near to it and the music almost very low or muted. Both my Dynacos have that transformer?chassis hum. There is no hum thru the speakers.
I have tried all sorts of experiments with switching out different outlets ect....
All 3 of my amps have the 2 prong old style plugs. Another thing I do is put a cast iron York 5 pound dumbell weight on the cages and it brings the hum down some but not like the Heathkit.
I live in a mobile home with more modern wiring than some apts. I used to live at. Everything looks up to code,is grounded, and there are enough outlets to keep any Hi-fi nut very happy. I think the Heathkit proves that.
There was a polarity outlet tip in the latest or 1 month ago Absolute Sound but I think the humming of the Dynas need some more attention than that test which I really have not tried with my multimeter yet.
So here is my question....Will your Humdinger work for my problem? If I was careful with it could it be returned if there was no improvement?
When I listen to music at a normal level you can't detect the hum. But like a Dog Whistle just knowing it's there is keeping my Heathkit on the play list knowing it's performing better.
Thanks for any info Frank, and or also Wayne and Mary.....I don't know who else works for ya but their alright....thanks Mark Korda.

avahifi · « **Reply #1 on:** 25 Feb 2017, 07:25 pm »

The Humdinger may work if your issue is low level DC on your AC power line.

Try it. If it works for you, great.

If not, our 30 day satisfaction guarantee applies, as it does on all AVA equipment.

Frank

Mark Korda · « **Reply #2 on:** 25 Feb 2017, 08:00 pm »

Hi Frank,
before I order one from you is there a simple test to see if I have unwanted DC on my AC lines or is the Humdinger the only way to know...I have a multimeter ...thanks Mark

Wayner · « **Reply #3 on:** 26 Feb 2017, 12:07 am »

It is not uncommon for laminated core and coil type transformers to have loose laminates and vibrate in synchronization to the 60 cycle pulses found in a power transformer. This was a common problem in the lighting industry, ballasts humming.

Since the Humdinger was designed to remove DC offset voltage in torodial transformers, and none of your amps have them (I'm assuming here that they were not modified by anyone along the way), I'd say the hum is mechanical by nature.

I suggest you examine the laminates on each transformer, looking for gaps in the laminations.

Wayner

Mark Korda · « **Reply #4 on:** 26 Feb 2017, 12:54 am »

Wayner, thanks for your honesty. I'll look more closely at the transformers to check for gaps and get back to you. The Heathkit has 2 transformers without housings or bells. They look cheap but they are dead silent? Thanks Wayne...Mark K.

avahifi · « **Reply #5 on:** 26 Feb 2017, 03:08 pm »

We have seen hum caused by low level DC in amps with standard iron core transformers here too, not just with toroids.

No easy way to determine if your hum issue is from DC or from a loose plate other than trying the amp on a known separate Ac line source. If it hums in one location but not in another it probablly is DC. If it hums in all locations it probably is bad transformer.

Please call me for more help. 651-330-9871

Frank

rcag_ils · « **Reply #6 on:** 27 Feb 2017, 09:25 pm »

If hum is mechanical from loose laminates, you can used vibration isolating material, place them between where the transformer make contact with the chassis. I did this to all my old Dyna 70 and Pas. You don't hear the hum coming through your speakers, but it's there, you'll notice the difference in sound after you isolate the noise from the chassis, and convert it into heat through the isolating material. I think the AVA transformers already have a piece under them, if I remember correctly.

rlee8394 · « **Reply #7 on:** 27 Feb 2017, 11:08 pm »

MArk,

My guess would be mechanical hum. You could try these for isolation as mentioned by others:

http://www.dynakitparts.com/dynakit-products/hardware/POWER-TRANSFORMER-ISOLATION-MOUNTS

If you insist on keeping the two Dynas, you may want to replace the original trannys with new ones.

http://www.dynakitparts.com/dynakit-products/transformers/PA060-transformer

http://www.dynakitparts.com/dynakit-products/transformers/PA-774-transformer

The amps and transformers will run much cooler as well.

-Ron

Mark Korda · « **Reply #8 on:** 28 Feb 2017, 12:23 am »

Hey guys,
You all have been a great help! Frank, I have tried my Dyna amps in different outlets and the hum is still there, very minimal but its there. Wayner, you may be right about the plates so I am not going to order the Humbug yet. I found a friend yesterday that is going to lend me a Emotiva AC bar that does the same thing more or less than the Humbug. Also Wayne your honesty saved that Humbug from making a cross country trip only to be returned as it would be used as a devise to troubleshoot and maybe not to buy. I hope Frank understands that; I don't like to have to send stuff back and I'm sure it's no fun for the seller. Plus I would not to that to friends and I'm saving my money for the Ultravalve.
Rcag-ils thanks for the isolation tip for transformers. For some reason I have been putting off the construction of a pair of Dyna Mark 3's. I finally have everything I need. Because of the hum issue in the other 2 amps I went to the hardware store and bought some brass washers that I thought of using with the transformer screws. Why?, I don't know......Enter Rlee 8394 with those mounts from Dynaparts. I bought some stuff from them recently and didn't even see those...thanks. I'm going to buy a handful of those and start building and fixing. It may be the Jack Benny way out but will eliminate 1 problem to get to the solution...thanks so much you guys...Mark.

avahifi · « **Reply #9 on:** 28 Feb 2017, 12:32 am »

Emovita? We tried one. Compared to HumDinger, it's less.

rcag_ils · « **Reply #10 on:** 28 Feb 2017, 02:40 am »

The Dynakitparts store isolation cost $6.00 a piece, that's too high for me, I'm sure you can substitute with other material and have the same result, I use the small isolators off a old turntable motor, I bought them new of course.

PS, the Heathkit AA-32 is a great amp, I have one too, other than Heathkit used the wrong paint on it's cover during that time, the paint tends to peel off.

Mark Korda · « **Reply #11 on:** 28 Feb 2017, 05:32 am »

Hi,
Frank, the Emotiva is just on loan for a test. Sorry about the name Hum Bug. It does seem to have a good ring to it though.
Rcag, I'm glad I read your response before I ordered those transformer shock absorbers...6 bucks a piece? I was needing 40 of them before I read your letter. That would of made Jack Benny turn around in his grave and has directed my project focus into a new direction. You can be damn sure I can (McGiver) some gizmo in there for cheap.
Rcag, the paint came right off my AA-32 cover. The Heathkit chassis cover with that tan paint seems to be totally rust free like stainless steel. I got some flat black used for grills at the hardware store and it looks better to boot...Mark K.

Mike-48 · « **Reply #12 on:** 28 Feb 2017, 07:10 pm »

I can't say if it will solve your particular problem, but I can say that the HumDinger is a great unit. I have 3 of them -- one feeding a Marsh amplifier in my desktop system, and two feeding the subs in my main system. In each case, the HumDinger solved an annoying hum, which is an absurdly common problem with hifi gear. I encourage you to try one.

rlee8394 · « **Reply #13 on:** 28 Feb 2017, 09:20 pm »

"The Dynakitparts store isolation cost $6.00 a piece..."

Actually it is $6.00 for a set of four. Not too expensive IMHO. On the other hand, if you choose to replace the transformer they are included for free.

-Ron

Mark Korda · « **Reply #14 on:** 1 Mar 2017, 02:57 am »

Hi,
thanks for tip Mike. If the Emotiva works I will get the Hum Dinger. The Emotiva is only on loan from a friend to test my outlet and amp. I have a funny feeling Wayne is right.
Rlee, I figured out the cost for 4 Dynakit transformer shocks and it was less than I had calculated..but
Holding a Mark 3 transformer in my hand there is no way those Dyna shocks will work. The transformer mounting tabs on the bells are slightly bendable. If you put 4 of those shock rigs on to mount the transformer the weight in the middle of the transformer would cause it to sag and soon contact the chassis. A better answer would be some sort of traced out rubber type gasket, with holes for wires and mounting screws...sort of like a head gasket on a car engine. I have some black stuff I bought from Parts Express I will try.
I did go to the hardware store and bought a couple rubber grommets and washers for about 10 cents each that looked just like the Dynakit ones before I figured out the latter.
One other experiment I want to try is to make that vibration gasket out of this 1/8 inch finish plywood I have here. I forgot what carpenters call it. Axe handles and baseball bats use wood to absorb vibration. My theory is that rubber feet might not transfer vibration but rather isolate it meaning it remains in the chassis rather than being disapated with wood. Maybe a wild idea....thanks you guys...Mark

sfox7076 · « **Reply #15 on:** 1 Mar 2017, 01:08 pm »

I use neoprene faucet washers to isolate. Very cheap and they work fine.

Mike-48 · « **Reply #16 on:** 1 Mar 2017, 03:22 pm »

Quote from: Mark Korda on 1 Mar 2017, 02:57 am

My theory is that rubber feet might not transfer vibration but rather isolate it meaning it remains in the chassis rather than being disapated with wood. Maybe a wild idea....thanks you guys...Mark

Yes, a wild idea! Don't forget, a baseball bat or an ax handle must support weight in motion. But this application is pure vibration control. There's a reason speaker surrounds, shoe inserts, Isopods, and other vibration-control pads are made from rubber-like material, not wood!
Rubber deforms readily, and in doing so, both isolates and absorbs energy.

If you're old enough to remember typewriters, you may also recall that one could buy foam-rubber pads to put under them to reduce the noise transfer to the desk, where it would radiate. They worked well. I can't imagine that a piece of wood would have worked. Can you? Yes, a wooden desk was quieter than a metal one, but the rubber really made a difference.

Wayner · « **Reply #17 on:** 1 Mar 2017, 04:34 pm »

Isolating transformers and their metal heatsinks from steel chassis may not be in the best interests of the transformer. Over-heating may be a concern as the chassis that holds the transformer may actually be dissipating a significant amount of heat off of the transformer.

Wayner · « **Reply #18 on:** 1 Mar 2017, 10:07 pm »

Mark,

I think you need to try the Humdinger before you start modifying your amp. If you ordered one tomorrow, you would have it early next week (its a quick ship item, in stock), you can find out before physical things are done. Its the next logical step if you haven't seen any signs of a physical cause.

Wayner

Mark Korda · « **Reply #19 on:** 2 Mar 2017, 12:25 am »

Hi Mike in NC,
Is that you standing next to a Mercury capsule? I'm a big space race fan. Anyway, if you think my wood idea is a little out there can I ask you if you ever got these green fliers in the mail from Mapleshade? If not they are on line. Their cd's are the best I have ever heard, just wish I liked the style of music more.
Wayne, I have to wait until this weekend before I move to getting a Hum Dinger. It's not just the Emotiva test but a friend I have not seen in a long time is planing to help me. I see what you mean about heat disapation with the transformers.
SFox. thanks for the tip but I still think you would need something as thick as the washers underneath the main body of the transformer to prevent vibrations..thanks guys...Mark.